Remotely interrogatable apparatus and method for detecting defects in structural members

Abstract

The apparatus and associated method of the present invention remotely detects structural defects in a workpiece by monitoring the electrical continuity of thin crack wires deposited on or within the workpiece in response to a communication from a remote interrogation device. As a crack, delamination or other structural defect forms or propagates in a structural member or other workpiece, a crack wire located in the vicinity of the crack breaks. In addition to the crack wires, the defect sensing apparatus includes a transponder and a discontinuity sensor for detecting a discontinuity along the crack wire. In order to inspect the workpiece, a maintenance technician positions a remote interrogation device in proximity with the workpiece under inspection. The interrogation signals provided by the remote interrogation device are received by the transponder and serve to power the defect sensing apparatus. Once sufficiently energized, the discontinuity sensor typically applies a voltage to one end of the crack wire and monitors the voltage level at the other end of the crack wire to determine the crack wire has broken, thereby indicating the presence of a crack, delamination or other defect. The discontinuity sensor reports the crack wire status via the transponder to the remote interrogation device for review by the maintenance technician. The defect sensing apparatus may be integral to a structural member or form one part of a reinforcement patch that is installed during a repair to monitor the structural integrity of a repaired structural member.

That which is claimed is: 
     
       1. A remotely interrogatable apparatus for detecting structural defects of a workpiece, said apparatus comprising: a conductive path extending across at least a portion of the workpiece; and   a communication device associated with the workpiece, said communication device comprising: a discontinuity sensor for detecting a discontinuity along said conductive path indicative of a defect within the workpiece; and   a transponder, responsive to said discontinuity sensor, for communicating with a remote interrogation device to thereby report structural defects detected within the workpiece.     
     
     
       2. A remotely interrogatable apparatus according to claim 1 wherein said conductive path includes a plurality of branches extending across different portions of the workpiece such that said conductive path extends from a first end common to each of the plurality of branches to a plurality of second ends associated with respective ones of the branches. 
     
     
       3. A remotely interrogatable apparatus according to claim 2 wherein said discontinuity sensor detects a discontinuity along any one of said conductive paths indicative of a defect within the respective portion of the workpiece, and wherein said transponder reports defects detected within any of the different portions of the workpiece. 
     
     
       4. A remotely interrogatable apparatus according to claim 1 wherein said communication device is a passive communication device powered by a remote interrogation signal. 
     
     
       5. A remotely interrogatable apparatus according to claim 1 wherein said communication device further comprises a memory device for storing an identification number assigned to said communication device. 
     
     
       6. A remotely interrogatable apparatus for detecting structural defects of a workpiece, said apparatus comprising: a conductive path extending across at least a portion of the workpiece, said conductive path including a plurality of branches such that said conductive path extends from a first end common to each of the plurality of branches to a plurality of second ends associated with respective ones of the branches; and   a communication device associated with the workpiece and coupled to said conductive path so as to detect a discontinuity along any one of the plurality of branches indicative of a defect within the workpiece, said communication device adapted to communicate with a remote interrogation device to thereby report structural defects detected within the workpiece.   
     
     
       7. A remotely interrogatable apparatus according to claim 6 wherein said communication device comprises: a discontinuity sensor for detecting the discontinuity along said conductive path; and   a transponder, responsive to said discontinuity sensor, for communicating with the remote interrogation device to thereby report structural defects detected within the workpiece.   
     
     
       8. A remotely interrogatable apparatus according to claim 6 wherein said communication device is a passive communication device powered by a remote interrogation signal. 
     
     
       9. A remotely interrogatable apparatus according to claim 6 wherein said communication device comprises a memory device for storing an identification number assigned to said communication device. 
     
     
       10. A method of remotely detecting defects within a workpiece, the method comprising the steps of: transmitting an interrogation signal from an interrogation device to a remote communication device associated with the workpiece;   detecting a discontinuity along a conductive path in response to the interrogation signal, wherein the conductive path extends across at least a portion of the workpiece and is coupled to the communication device, and wherein the discontinuity is indicative of a structural defect within the workpiece; and   reporting a detected structural defect to the remote interrogation device.   
     
     
       11. A method according to claim 10 wherein said detecting step comprises the steps of: applying a voltage to a first end of the conductive path; and   monitoring a voltage level appearing at a second end of the conductive path to determine if the conductive path is continuous.   
     
     
       12. A method according to claim 11 wherein the conductive path includes a plurality of branches such that the conductive path extends from a first end common to each of the plurality of branches to a plurality of second ends associated with respective ones of the branches, and wherein said monitoring step comprises monitoring the voltage levels appearing at each of the second ends of the conductive path to determine if each of the branches is continuous.